1. Field of the Invention
The present invention relates to a color image forming apparatus and a development method-for the color image forming apparatus for forming developed images in different colors on a plurality of photosensitive drums using developing units having different-colored developers respectively, obtaining a color image by multiple-transfer of color-superimpostion of the different-colored developed images on a paper sheet, collecting the respective developers remaining on the photosensitive drums in the respective developing units after end of transfer, and recycling them.
2. Description of the Related Art
Among color image forming apparatuses such a copying machine of an electrophotographic type and a printer, as a one for speedup of image forming, a color image forming apparatus, for example, of a two-piece tandem type is known that a plurality of image forming stations are arranged along the conveying path so as to form images for each color, and developed images in different colors respectively are formed on the photosensitive drums at the respective image forming stations, and a color image is obtained by executing multiple-transfer of sequential color superimposition of developed images in different colors on a paper sheet to be conveyed on the conveying path in synchronization with each developed image.
Conventionally, in such a color image forming apparatus of a tandem type, a phenomenon occurs that at an image forming station on the downstream side of the conveying path, at the time of multiple-transfer of a developed image on a paper sheet on which a developed image is transferred already on the upstream side, a part of the developed image formed at the image forming station on the upstream side is reversely transferred from the paper sheet onto the photosensitive drum side. Therefore, at the image forming station on the downstream side of the conveying path, the developer at the image forming station on the upstream side is mixed in the residual toner on the photosensitive drum after end of transfer.
Therefore, when the residual toner cleaned and removed is recycled, the original color cannot be obtained due to mixture of the developers and the display dignity of color images is lowered. Therefore, in a color image forming apparatus of a tandem type, conventionally, the residual toner on the photosensitive drums after end of transfer is removed by a cleaning unit without recycling it, then collected in a waste toner box, and disposed of by a user periodically after the waste toner box becomes full.
However, from the viewpoint of profitability of cost reduction by saving of toner consumption and from the viewpoint of environmental protection countermeasures such as practical use of resources and reduction in industrial wastes, recycling of toner has been desired recently.
On the other hand, a color image forming apparatus for collecting toner remaining on a photosensitive drum in a developing unit after end of transfer and recycling it is disclosed in Japanese Patent Application Laid-Open 9-236962. However, this color image forming apparatus for recycling toner originally uses a single photoconductor, forms a developed image in an optional color for each rotation of the photoconductor, and superimposes the color on a transfer paper, so that forming of a color image requires a lot of time and the color image forming apparatus is not suited to speedup. Further, the residual toner after transfer is collected from the photoconductor surface once by a cleaning member and then adhered again into the area independent of image forming on the photoconductor, thus the residual toner readhered onto the photoconductor is collected in the developing unit. Therefore, it is necessary to install an area for readhering the residual toner on the photoconductor and execute a residual toner readhesion process for the photoconductor separately from the developed image forming process, so that miniaturization of the photoconductor and speedup of the process will be prevented.
Therefore, in a color image forming apparatus of a tandem type for speeding up the color image forming process, it is desirable to collect residual toner without preventing speedup of the image forming process, obtain a good color image without reduction in the display dignity due to mixture of developers at the time of recycling of the collected residual toner, decrease the running cost, and contribute to environmental protection countermeasures.
An object of the present invention is to provide a color image forming apparatus of a tandem type for recycling residual toner without reduction in the display dignity, decreasing the cost, and contributing to environmental protection countermeasures.
Another object of the present invention is to provide a color image forming apparatus of a tandem type for collecting and recycling residual toner without reducing the process speed.
According to the present invention, a color image forming apparatus is provided, and the apparatus is composed of a plurality of recording medium arranged along a conveying path for forming electrostatic latent images, a plurality of developing units installed respectively in the neighborhood of the plurality of recording medium for feeding developers having different lightness to the respective electrostatic latent images formed on the plurality of recording medium and forming developed images, a plurality of transfer units for multiple-transferring the developed images formed respectively on the plurality of recording medium sequentially on a material to be transferred which is conveyed along the conveying path, and a plurality of collectors for collecting the respective residual developers on the plurality of recording medium after passing the transfer units in the plurality of developing units respectively, and among the plurality of developing units, the developing unit having the developer with lowest lightness compared with the developing unit having the developer with highest lightness is installed in the neighborhood of the recording medium arranged on the downstream side of the conveying path.
Further, according to the present invention, a color image forming apparatus is provided and the apparatus is composed of a plurality of recording medium arranged along a conveying path for forming electrostatic latent images, a plurality of developing units installed respectively in the neighborhood of the plurality of recording medium for electrostatically feeding developers having different lightness to the respective electrostatic latent images formed on the plurality of recording medium, forming developed images, and electrostatically collecting residual developers adhered to the recording medium, and a plurality of transfer units for multiple-transferring the developed images formed respectively on the plurality of recording medium sequentially on a material to be transferred which is conveyed along the conveying path.
Further, according to the present invention, a color image forming apparatus is provided and the apparatus is composed of a plurality of recording medium arranged along a conveying path for forming electrostatic latent images, a plurality of developing units installed respectively in the neighborhood of the plurality of recording medium for feeding developers having different lightness to the respective electrostatic latent images formed on the plurality of recording medium and forming developed images, a plurality of transfer units for multiple-transferring the developed images formed respectively on the plurality of recording medium sequentially on a material to be transferred which is conveyed along the conveying path, cleaning members for removing the respective residual developers on the plurality of recording medium after passing the transfer units, and additionally a plurality of collectors having developer conveying members for conveying the residual developers removed by the cleaning members to the plurality of developing units.
Further, according to the present invention, a developing method for a color image forming apparatus is provided, and the method is composed of a developing step of electrostatically feeding developers having different lightness respectively to electrostatic latent images formed on a plurality of recording medium arranged along a conveying path using developing members and forming developed images, a transfer step of multiple-transferring the developed images on the plurality of recording medium sequentially on a material to be transferred which is conveyed along the conveying path, and a collection step of electrostatically collecting the residual developers remaining on the plurality of recording medium using the developing members after ending of the transfer step, and the developing step is executed for the recording medium arranged on the upstream side of the conveying path using the developer with highest lightness, and the developing step is executed for the recording medium arranged on the downstream side of the conveying path using the developer with lowest lightness.
Further, according to the present invention, a developing method for a color image forming apparatus is provided, and the method is composed of a developing step of electrostatically feeding developers having different lightness respectively to electrostatic latent images formed on a plurality of recording medium arranged along a conveying path using developing members and forming developed images, a transfer step of multiple-transferring the developed images on the plurality of recording medium sequentially on a material to be transferred which is conveyed along the conveying path, and a collection step of removing the residual developers remaining on the plurality of recording medium using cleaning members after ending of the transfer step and additionally conveying the residual developers removed toward the developing members, and the developing step is executed for the recording medium arranged on the upstream side of the conveying path using the developer with highest lightness, and the developing step is executed for the recording medium arranged on the downstream side of the conveying path using the developer with lowest lightness.